The present invention relates to an intake system or arrangement for an internal combustion engine, integrally incorporating a throttle valve for regulating the flow rate of intake air delivered to cylinders of the internal combustion engine, and an air flow meter for determining the total flow rate of intake air flowing through an intake pipe by measuring local flow rate of the intake air.
Japanese Patent Provisional Publication (Kokai) Nos. 59-105519 and 59-122915 disclose intake systems.
In those known intake systems, a hot-wire flow meter is disposed within a throttle body at a position where the measuring accuracy of the hot-wire flow meter will not be deteriorated even if the air flow speed distribution within the throttle body varies according to the degree of opening of the throttle valve.
The inlet of a bypass pipe for delivering bypass air therethrough around the throttle valve to the engine to promote the warm-up of the engine, and the inlet of a bypass for delivering bypass air therethrough around the throttle valve to the engine to maintain the engine idling speed at a desired value during idling are provided in the throttle body upstream the throttle valve. Accordingly, the air flowing through the bypasses also causes the variation of the flow speed distribution of the air flowing through the throttle body.
Nevertheless, in those systems, only the influence of the movement of the throttle valve on the flow distribution is taken into account, and hence the influence of air flowing through the bypasses on the flow speed distribution within the throttle body deteriorates the accurate measurement of flow rate.